Method of generating vapor



. V March 31, 1 936. -H. GLEICFIMANN 2,035,879

' MEILTHOD OF GENERATING VAPOR Filed Sept. 20, 1953 Patented Mar. 31,1936 PATENT. OFFICE METHOD OF GENERATING VAPOR Hans Gleichmann,Falkenhain, near Spandau, Germany, assignor to Siemens-SchnckertwerkeAktiengcsellschai't, Berlin-Siemensstadt, near Berlin, Germany, acorporation of Germany Application September 20, 1933, Serial No.690,262 In Germany June 14, 1932 12 Claims. (Cl. 122-247) This inventionrelates to improvements in the art of generating steam, particularly insteam generators of the type in which there is a forced passage of theoperating medium therethrough.

Experience has shown that great difflcultiesare experienced in theoperation of forced flow multitubular steam generators due to thepercentage of salt or salts in the water which is to be evaporated. Togenerally explain such difliculties the conditions prevailing in a drumboiler, i. re. a boiler with natural circulation, will be firstexplained. In a drum boiler, there is a substantial water capacity andsuch capacity is maintained constant by hand or automatically by feedwater regulators. The feed water, even though it is chemically preparedor obtained from evaporators, is never completely pure, but containscertain soluble impurities. As soon as the water evaporates theseimpurities (salts) remain in the water which .has undergone noevaporation. The water contained in the boiler will consequently take upthe salt constituents gradually. The ultimate result is that the watercontains a substance in the nature of a lyewhich with time, constantlyincreases in strength and which may then be drained from time to time orcontinuously so as to thereby maintain the water contained in the boilerto a given concentration of the lye. In the case of a multi-tubularboiler with forced passage of the operating medium therethrough, thereis no drum. and therefore there is not the possibility of automaticcleaning. In contradistinction in such boilers the water is forced by apump into the system at one end of the tuberand leaves the other end oi'the tube as vapor. Evaporation occurs intermediate the ends of thetube. There is no substantial storage of water in the tubular system andaccordingly there is not the possibility of draining oiT water graduallyenriched with lye as in the case of the boilers of the drum type.

. The result is that in such boilers there is a zone on the inner tubewalls which is not sufliciently supplied with water, and salts, asexperiments have shown, deposit in this zone until the vapor hasattained a given degree of superheat. So long as the number of heatunits imparted per unit of heating surface of the tubes is small suchdeposit of salts may form a considerable layer without subjecting thetubes to the danger of being burnt. n the other hand the conditions areentirely different in cases where a great number of heat units per unitof heating surface is imparted to the tubes as is usua .0 instance, withmodern radiation boilers. With the latter types of boilers a relativelyslight settling of salt in the tubes contributes to a comparativelyrapid destruction of the tubes. Since it is not possible with tubularforced flow boilers to ex- 5 tract the salt-like impurities from thefeed water, other methods and means must be resorted to for boilers ofthe type which employ a heating surface to which heat of high intensityper unit of surface is imparted, in order to counteract and minimize theefiects oi the settling oi salt in the tubular system.

An object of the present invention resides in the provision of a novelmethod of converting an operating medium from the liquid state to avapor state in a forced flow generator and in providing for theminimizing of salt deposit difficulties in such generation of vapor.

A further object of the present invention resides in the provision of anovel multiple stage heating method for generating vapor in which theheating effects are such that the dangers attendant upon salt depositsare minimized.

A further object of the present invention resides in the provision of anovel method of converting an operating medium from the liquid state toa vapor state in a forced flow generator and in providing for theminimizing of salt deposit dimculties in such generation of vapor.

A further object of the present invention re- 3( sides in the provisionof a novel multiple stage heating method for generating vapor in whichheating effects are such that the dangers attendant upon salt depositsare minimized.

Further and other objects of the present invention will behereinafterset forth in the accompanying specification and claims andshown in the drawing which shows by way of'illustration a preferredembodiment and the principle thereof and what I now consider to be thebest -mode in which I have contemplated of applyby a stage of heatabsorption in order to effect complete vaporization at substantiallyconstant temperature, the latter stage being the zone in which thefluidis converted from liquid to vapor ".5

account of deposition of salts. Therefore, from a broad point of view,my invention comprehends any arrangement of forced fiow type of boilerwherein the medium at the saturated temperature is converted to steamand evaporation is completed in the contact or convection portion of theheating space to 'avoid injury to the tubing on account of saltdeposits.

'In the improved boiler and in accordance with the preferred andspecific method of the present invention, the heat absorbing surface inwhich the evaporation takes place is divided into two portions receivingdifferent amounts of heat supply per unit of heating surface, 1. e. thegenerator is divided into a heat absorbing surface portion to which heatof higher intensity is imparted and in which, computed with respect tothe entire extent of the heat absorbing surface portion, the percentageof liquid exceeds the percentage of steam in the operating mediumandinto another heat absorbing surface portion to which heat of lowerintensity is imparted and in which conversely the percentage of vaporexceeds the percentage of liquid. With such generator it has been provenalso practicable to add to the heat absorbing surface portion to whichheat of lower intensity is imparted also, the first portion of thesuperheater. This'is preferably done because first slightly superheatedsteam may 40 still contain a certain amount of water, and secondlybecause such arrangement provides,

- upon variation in load and upon the shifting of the zone ofevaporatlon,a sort of safety zone, which safety zone maintains thezone-of evaporation within the zone of heat of lower intensity per unitof heating surface.

In the accompa y drawing:

Figure 1 illustrates diagrammatically, the conditions prevailing in asteam generator with sub-divided heating surfaces for the evaporation ofthe operating medium according to the present invention; In Fig. 2 isshown a cross-section of a steam generator embodying features of thepresent invention.

' Referring first to diagrammatic Fig. 1, three fundamental zones in aforced flow steam generator should'first be taken into consideration, i.e. the pre-heating zone W, the zone of evaporation V and the zone ofsuperheat U. In the zone of pre-heating, sensible heat is imparted tothe operating medium. In the zone V the heat of evaporation isimpartedthereto and in the zone U the superheat is imparted to such medium. Onentering the zone V the operating medium is substantially 100% liquidand 0% steam, whereas on ent invention this zone is not supplied withheat of the relatively high intensity. This isiiaccomacute-2a plishedpreferably by subdividing the heat absorb ing surface portion V intosections a and b. The

section a of the heating surface is supplied with heat of relativelyhighintensity and the section b supplied with heat of relatively lowintensity. 5 While the specific method described herein preferablyinvolves dividing'the heat absorbing surface V into sections a and b,the section a being heated in the high intensity or radiant heat portionof the heating space and the section b being supplied with heat ofrelatively low intensity in the convection or contact portion of theheating space, it is to be understood that, so far as my invention isconcerned, the means of applying heat in this way, although desirable,is not essential, my invention comprehending the arrangement of thepreheating zone W, the zone of conversion V, and the zone ofsuperheating U,

whether the evaporation zone V is located partly towards the liquidside.

in the radiant space and partly in the contact 20 space or entirely inthe latter, the only requirement being that at least the finalevaporation and preferably a part of the superheating shall be completedin the contact or convection portion of the heating space so that saltdeposit difilculties may be overcome. In computing the proportions ofthe heat absorbing surfaces for evaporating a certain amount of heatingmedium, the heat absorbing parts or sections are so proportioned withrespect each other and to the total extent of heat absorbing surfacethat the percentage of liquid exceeds the percentage of steam in the asection and conversely in the b section the percentage of steam exceedsthe percentage of liquid. The dangerous zone G comprises,as shown inFig. 1, not only the section b of the evaporating zone V, but also thesection 0 which constitutes a part of the heat absorbing surface of thesuperheater. How much of the total surface should be of the b'type towhich heat of the relatively lower intensity should be imparted and howmuch should be of the a type to which heat of relatively higherintensity is to be imparted will depend upon the particular conditionsupon which the steam generator is to operate. According to previousexperlence, the zone of subdivision of the two heat absorbing surfaceportions a and b may be shifted in the direction of progressiveevaporation towards the steam side so that the a section may terminateand the b section commence at a point 50 where the system containsheating medium which is about 10% liquid (note e Fig.1) At this pointthere is approximately steam in the tubular system. The exact point ofsub-division of the heating sin'i'ace between a and b is a matter to be5 ascertained for each generator. In some cases, the sub-division pointmay be shifted towards the steam side and in other cases it may beshifted The later shift of the sub-division point towards'the liquidside will be convenient and'preferable if the generator operatingconditions are such that in operation there is a considerable variation,shift, or displacement of the evaporating zone V, as for instance, withvariations of load, variations of feed water temperature and variationsof furnace temperature and conditions. The superheating' surface a andparticularly its section which is to be supplied with heat of relativelylow intensity due l to possible water in the entering steam, may bedetermined in the same manner according to the operating conditions..Refen'ing now'to Fig. 2, is shown one" and a preferred embodiment ofasteam generator 75 which incorporates the features of the presentinvention. 7

The steam generator shown may be of a form in which the products ofcombustion are derived from pulverized com. The pulverized coal isconveyed from a bunker l0 by'a distributing feed screw ll into theburner piping and finally discharged'at the burner nozzle l2. The feedscrew may be driven by'a motor l3 and the speed ofv the motor and therate of delivery of the pulverized coal may be varied by manipulating arheostat IS. The air for supporting combustion may .be introduced intothe generator by means of a blower I 6 which delivers the air throughpiping H to the burner nozzle l2. The blower has an inlet at l8 andpreferably and usually the entering air is pre-heated in the customarymanner. The blower it may be driven by a motor I9 and the speed of suchmotor may be varied and regulated by a rheostat 20. The combustion gasesevolved from the pulverized fuel flame take the path shown by the arrowsin Fig. 2, that is to say, they divide at the exit end of the furnace orcombustion chamber 2| and the divided cur-. rents 22 and 23 passthrough'supplemental heat absorbing chambers 24 and 25. The gasesleaving the top of these chambers again unite and are discharged fromthe generator by a propeller type of fan 26. This fan may be driven inany desired manner as by means of a motor 21 and the speed may be variedby ineans of a rheostat 28.

The medium to be heated such as water or other liquid is forced into thegenerator by means of a pump 29. The pump is driven by a suitable motor30 provided with a rheostat 3| for con-. trolling the speed of drive.From the pump the medium to be heated in the generator passes to andthrough a distributing header 32. Tubular heat absorbing elements of thegenerator are connected to such header 32. Such tubular elements extendinto and preferably line the combustion chamber 2|. This particular heatabsorbing section of the generator is designated 33a and 34a and this isthe section of the heat absorbing surface of the generator to which heatv of relatively high intensity is imparted. The

heat absorbing sections 33a and 34a receive high intensity heatprincipally by radiation and from such sections the medium to be heatedpasses to the tubular sections 35b and 36b which are disposed in theheat absorbing chambers 24 and 25 and arranged in such manner therein asto receive heat by convection from the hot gases. Such sections aresubstantially shielded from the effects of high intensity radiant heat.Each of these tubular sections 35b and 36b accordingly receives heat ofrelatively lower intensity and the heat load in the generator at thispoint is relatively less than the heat load in the combustion chamber 2|where heat transfer is effected to the tubular elements .by highlyintense radiant heat. After pwsing the sections 35b and 35b the mediumto be heated passes through tubular heat absorbing sections 310 and 380and from such sections it passes out of the generator at the collectingheader. 39; The sections 310 and 38c likewise .receive high intensityradiant heat, beingadisposed within and preferably lining the-walls ofthe.combustion chamber 2|.

- The generator according to the present invention has its sections soproportioned and is operated in such a way that in the sections 33a and34a the liquid content .of the medium predominates over the steamcontent and high in-- tensity heat is received thereby so that this heatabsorbing section operates with a relatively high heat load.

The operating medium in the sections 33a and 34a has heat of relativeh!high intensity applied thereto to raise its temperature to theevaporation point and then to effect the progressive transition ortransformation of the medium from the liquid to the vapor state until apoint is reached such that the medium is partially vaporized' and theamount of vapor predominates over the residuum of liquid. Thus, it willbe seen that the heating surface 33a; 34a may be used to effect heatingof the liquid, if the temperature of liquid supplied thereto is belowthe saturation temperature, followed by progressive vaporization of theliquid, or such heating surface may be used entirely to effectprogressive vaporization if liquid atsaturation temperature is suppliedthereto. The partially vaporized operating medium is supplied from theheating surface 33a, 34a to the heating surface 35b, 36b, the latterheating surface having heat of relatively lower intensity appliedthereto so as to complete transformation of the operating medium intothe vapor state and preferably to effect an initial stage ofsuperheating. As hereinbefore pointed out, salts are deposited orconcentrated in the heating surface during the latter part of conversionfrom the liquid to the vapor state and during the initial portion ofsuperheating, this being the danger zone G referred to in connectionwith Fig. 1. Therefore, as the heating surface 35b, 36b is so arrangedin the'furnace as to be subject to heat of a relatively low intensity,it will be apparent'that the danger zone, such as indicated in Fig. 1.may be located in such manner that the tubing will not be injured eventhough salts should be deposited therein. Applying the method of steamgeneration diagrammed in Fig. l, the preheating stage W is effected tothe extent required in the heating surface 33a, 34a or such heating maybe efiected in any other suitable heating surface. The stage ofvaporization V is shown as comprising a. first part a wherein thepercentage of liquid predominates over the percentage of vapor and thesecond part b wherein the percentage of vapor predominates over thepercentage of liquid. The first part, a, of the vaporization stage iseffected in the radiant heating surface 33a, 34a. The latter part, b, ofthe vaporization stage and the initial part. c, of superheating, isefiected in the heating surface 35b, 36b, subject to heat of relativelylow intensity. The vapor, preferably superheated to some extent, issupplied from the heating surface 35b, 36b to the heating surface .310,380 wherein it is superheated. As illustrated. the latter heatingsurface is also preferably sub-' ject to heat of relatively highintensity.-

The sections 31c and 38c constitute the superheating:sections orportions andin these sections high intensity heat is imparted. Also thethe medium will be entirely in the vapor state,

.. temperatures, i'uelconditions, etc.

content and in this stage heat will be supplied at high intensity andthe heat loadwill be relatively high. In the b section or sections thevapor content will pre-dominate over the liquid content, the heatingefiect in this stage will be relatively lower and in this stage the heatload will be relatively low. In the c section .or sections the heat willbe supplied at high intensity and the heat load will again be relativelyhigh.

The generator, so proportioned, may then be operated in such a way as,to maintain such operating conditions during the generationof steam andduring the transition of the operating .me-

. dium from a liquid to the vapor state and during the successiveheating stages.

It will be understood that the generator shoul be so operated that thedangerous zone where evaporation occurs with the steam pre-dominating incontent over the liquid will be maintained inthe 35band 36b sections.

In the operation of the generator difllculties attendant upon saltdeposits may be minimized and obviated by properly initially designingthe various sections and operating the generator to maintain the abovedescribed evaporating conditions. r

In the generation of steam with the generator sections properlyinitially designed, the improved operating conditions may be maintainedunder various steam generating conditions by eil'ecting merely a. properadjustment of the heat supply and of the feed water supply. The variousrheostats provide for'the making of these adjustments for differentsteam outputs, feed water From the foregoing, it will be apparent that Ihave'devised a boiler'of the forced fiow typewherein diiHculties' onaccount-of salt deposition are overcome, this being done by having atleast that portion of the heat absorbing surface wherein vaporization ofmedium at the saturated temperature is completed, located in the contactor convection portion of the heating space which is at such a low gastemperature that the tubing will not be injured even though depositionof salts should occur. While I disclose herein a specific arrangementwhere the zone of vaporization of the mediumjat the saturatedtemperature is carried on both in the radiant and contact portions, itwill be obvious tha the general requirement 01 completion of. varization of medium at the saturated temperature in the contact portionmay be carried out in this way or I the entire vaporization zone may belocated in the contact or convection portiomof the heating space subjectto relatively low intensity heat.

The present application constitutes a continuation in part of mycopending application, Serial No. 655,805, filed February 8, 1933,, forSteam generators. 1

WhatIclaim is: l. The method of converting a liquid operating medium tosuperheated vapor in a forced flow tubular steam generator and ofminimizing the'difilculties due to salt deposits in the tubes in theevaporating zone, which comprises effecting the transition of the liquidto a superheated vapor in three stages, in one stage imparting heataosaave.

, ing the medium absorb heat in aplurality of zones of heat absorption,in one zone,-raising the temperature of the medium in the liquid stateto the point of vaporization and, in asecond zone, progressivelyincreasing the vapor content and decreasing the liquid content of themedium at said temperature, the second zone including a first stage suchthat, at the end thereof, there is sufiicient medium in the liquid stateto carry salts in solution, and aisecond stage wherein the residuum ofliquid with salts in solution is vaporized by heat of such relativelylow intensity that in- Jury to heating surface of said second stagehaving salts deposited thereon will be minimized.

3. The'method of converting water serving as operating medium into steamin a forced-flow sorb heat in a plurality of zones of heat absorption,in one 'zone, raising the temperature or the medium in the liquid stateto the point of vaporization and, in a second zone, progressivelyincreasing the vapor content and decreasing the liquid content of themedium at said temperature, the second zone including a first part suchthat, at the endthereof, there is sufilcient residuum of medium injtheliquid state to carry salts in solution and a second part wherein saidresiduum or liquid is vaporized; heatjof such relatively high intensitybeing used of heat absorption that heating surface having saltsdeposited thereon would be injured, and the second part of theevaporation zone being effected by heat of such relatively low intensitythat heating surface thereof having salts deposited thereonincident tovaporization will not beiniured. 4. The method of. converting waterserving as operating medium, into superheated steam in a forced-flow.tubular steam generator and of due to salt deposits, which a secondzone, progressively increasing the vapor content and decreasing theliquid content of the medium at the vaporization temperature, the secondzone including a first part such that, at the 'end thereof, there is,sufiicient residuum of medium in the liquid state to carry salts insolution and a second part wherein the residuum of liquid is vaporized,heat of such-relatively high intensity being used to efiect said firstzone of heat absorption and said first part of the second zone 01' heatabsorption that heating surface thereof having salts deposited 'thereonwould .be injured and the secondlpart of the second zone being eifectedby heat of-such relatively'lo'w inposited thereon will not be injured.

to effect said first zone in one zone, raising the temperature ofthemedium a liquid state to they-point of vaporization and, in

5. The method of converting water serving I as operating medium intosuperheated steam in a forced-flow tubular steam generator and ofminimizing dimculties due. to salt deposits incident 2,08 5,879 toevaporation, which comprises having the medium absorb heat in aplurality of heat absorption zones, in one zone, raising the temperatureof the medium in the liquid state to the point of vaporization and, in asecond zone, progressively increasing the. vapor content and decreasingthe liquid content of the medium at said temperature, the second zoneincluding a first part such that,

at the end thereof, there is sufiicient residuum of medium in the liquidstate to carry salts in solution and a second part wherein the residuumof liquid is vaporized, and, in a third zone of heatabsorption,superheating the vapor, heat of such relatively highintensity being used to effect said first zone of heat absorption thatheating surface thereof having salts deposited thereon would be injuredand the second part of said second zone and the initial portion of thethird zone being effected by heat of such relatively lowintensitycontent and decreasing-the liquid content of the that heatingsurface thereof having salts deposited thereon would be injured and thesecond part of the second zone being efiected by heat of such relativelylow intensity that heating surface having salts deposited thereon willnot be injured.

7. The method of converting water serving as operating medium intosuperheated steam in a forced-flow tubular steam generator and ofminimizing difliculties due to salt deposits, which comprises having themedium absorb hat in a plurality of zones of heat absorption, in onezone,

raising the temperature of the medium in the liquid state to the pointof vaporization, in a second zone, vaporizing the liquid in first andsecond stages, and, in a third zone, superheating the vapor in first andsecond stages, the medium being partially vaporized in the first stageof the second zone such that, at the end of such first stage, there issufiicient residuum of medium in the liquid state to carry salts insolution and the residuum of liquid being vaporized in the second stageof the second zone, heat of such relatively high intensity being used toeffect said first zone and the first and second stages of said secondand third zones, respectively, that heating surface thereof having saltdeposits thereon would be injured and the second stage of said secondzone and the first stage of the third zone being effected by heat ofsuch relatively low intensity that heating surface thereof having saltsdeposited'thereon will not be injured.

8. The method of converting water serving as operating medium into steamin a forced-flow steam generator so as to minimize difliculties becauseof salts" deposited incident to vaporization which comprises subjectingthe medium to a first stage of heating to raise the temperature thereofto the evaporation point and then to progressively effect transition ofthe medium from the liquid to the vapor state until the medium ispartially vaporized so that, at the end of the first stage, there issufficient medium in the liquid state to carry salts in solution, theintensity of heat for the first stage being relatively so high thatheating surface having salts deposited thereon would be injured, thenwithdrawing the medium in vapor and liquid states from the first stageand away from effects of the high intensity heat, and then subjectingthe medium to a second stage of heating to convert said residuum ofmedium in the liquid state into vapor, the intensity of heat of thesecond stage being relatively so low that heating surface having saltsdeposited thereon will not be injured.

9. The method of converting water serving as operating medium intosuperheated steam in a forced-flow steam generator so as to minimizedifiiculties on account of salts deposited on heating surface incidentto completion of vaporization which comprises subjecting the medium to'afirst stage of heating to raise the temperature thereof to theevaporation point and then to progressively efiect transition of themedium from the liquid to the vapor state until the medium is partiallyvaporized so that, at the end of the first stage, there is suflicientmedium in the liquid state to carry salts in solution, the intensity ofheat of the first stage being sufiiciently high that heating to convertsaid residuum of medium in the liquid state into vapor and to superheatthe vapor, the intensity of heat for the second stage being suflicientlylow that injury to heating surface having salts deposited thereon isminimized.

10. The method of converting water serving as operating medium intosuperheated steam in a forced-flow steam generator so as to minimizediiliculties due to salts deposited incident to vaporization and whichcomprises subjecting the medium to high intensity heat in a first stageofheating to raise the temperature of the medium to the evaporationpoint and then to progressively increase the vapor content and decreasethe liquid content until, at the end of the first stage, there issuflicient residuum of medium in the liquid state to carry saltsinsolution, withdrawing the medium in the vapor and liquid states from theefiect of the relatively high intensity heat, subjecting the withdrawnmedium to relatively low intensity heat in a second stage of heating inorder to convert-said residuum of liquid into vapor, and superheatingvapor received from the second stage by a third stage of heating withheat at relatively high intensity.

11. The method of converting water serving as operating medium intosteam in a forcedflow steam generator so as to minimize difficulties dueto salts deposited on heating surface incident to completion ofvaporization which comprises subjecting the medium to a first stage ofheating by the application of heat of relatively high intensity to raisethe temperature of the medium to the evaporation point and then to 6progressively increase the vapor content and decrease the liquid contentofthe medium until,

at the end of the first stage, there is suflicient medium-in the liquidstate to carry salts in solution, withdrawing the medium in the liquidand vapor states from the first stage and away from the eflects of therelatively high intensity heat, subjecting the withdrawn liquid andvapor to a second stage of heating by the application of aoaaavo ingmedium into vapor in tubular heating surface comprising supplying mediumunder pressure to the surface for e therethrough, providing heat of suchrelatively high intensity that heating surface containing salt depositswould 5 be injured thereby and heat of such relatively low intensitythat heating surface containing salt deposits would not be injuredthereby, ap-

plying the heat of relatively high and low intensities to the operatingmedium flowing through 10 the heating surface to raise the temperatureof such medium to the evaporation temperature and then to effect theprogressive transition of the medium at that temperature from the liquidto the vapor state, thelatter part at least of said 15 step oftransition being effected by the relatively low intensity heat.

' HANS GLEICHMANN.

